SHA-1
From The ECRYPT Hash Function Website
1 General Description
SHA-1 is an iterated hash function. It can be used to
compute a 160-bit hash value for messages having a length of less
than 
bits, cf. FIPS 180-2 Secure Hash Standard.
As most iterated hash functions, SHA-1 applies MD strengthening.
1.1 Compression Function
The compression function processes input message blocks of 512 bits and
produces a 160-bit chaining value. The compression function of
SHA-1 basically consists of two parts: the message expansion and
the state update transformation. The chaining variable 
(iv in the first iteration) is added to the output of the state update transformation (feed forward). This is graphically
illustrated in
